A process is disclosed for purification of sewage by biological means.
A significant problem connected with sewage disposal is that the sewage contains dissolved phosphorus and nitrogen which is difficult to separate from the fouled water. The elements in question pollute to a high degree and are harmful to the environment; ample demonstration of such pollution, for example, would be the problem of eutrophic activity which causes the abnormal reproduction of algae, in lakes and along the coasts at river estuaries, as a result of river water being laden with industrial and urban waste. It has been recognized for some time that cellulose provides a source of the carbon which is essential to the growth of cellulolytic micro-organisms; the absorption of nitrogen and phosphorus is a feature of the growth of such micro-organisms. This natural process is already being exploited, for instance, in the production of re-utilizable `bio-mass` energy sources from cellulose-rich refuse, the cellulose content of which must be removed. Such processes are disclosed in a number of patents --viz, U.S. Pat. No. 2,282,010, U.S. Pat. No. 4,461,708, DE No. 2227840 and U.S. Pat. No. 3,462,275. The cellulolytic process is also employed for stabilizing, and deodorizing and conditioning purified muds and fresh livestock sewage destined for agricultural use and for feed. Such a process is disclosed in FR No. 2260550.
The main object of the process disclosed is that of bringing about a drastic reduction in the phosphorus and nitrogen content of sewage.
The process also has the advantages of being highly economical and of providing by-products in the form of phosphorus- and nitrogen-rich fertilizer.
The aim and advantages thus stated are realized by the biological sewage-treatment processs disclosed, which is characterized in that it envisages contact brought about in aerobic conditions between the sewage and the cellulosic matter, for a given length of time, in the presence of cellulose-devouring heterotrophic micro-organisms.
Existing processes for the purification of sewage by biological means are classifiable under two basic types, according to whether the prevailing activity is aerobic or anaerobic. Such processes generally envisage a number of stages substantially comprising a first sedimentation stage to settle the more consistent solids, a second stage constituting treatment proper, and a third stage in which the muds are clarified and settled. Purified water is then drawn off whilst a proportion of the muds is recycled back to the second stage, the remainder being removed and utilized in the production of fertilizer. Processes of the above type may be continuous, or otherwise. The prior art further embraces a process for purification of sewage, disclosed in U.S. Pat. No. 4,039,438. Such a process employs cellulose in an anaerobic process whereby denitrification is implemented by elimination of the nitrogen content; however, no provision is made for the elimination of phosphorus, which is an element in sewage responsible for considerable pollution.